Updating hydrologic studies and the impact on hydraulic design

Flood events causing damages, fatalities, trigger new flood protection studies. Updated hydrologic study conforming with recent develop¬ments is required. Implementation of 2007/60/EU Directive led to Preliminary Flood Risk Assessment and Flood Risk Management Plans, establishment of related guidelines and point precipitation IDF relations for all stations in Greece, often giving higher rainfall depths. Use of the CN method for hydrologic losses gives more than proportional increases in the resulting discharge predictions. Comparing past and future conditions (2000-2018) has been facilitated by available landcover data through the Copernicus program, while designer's judgment is still needed to predict further trends in land practices/ urban development. Evaluation of climate change effect is often required for project financing. Main issues are sea level rise, increase of precipitation extremes, associated landslide risk. Current predictions involve high uncertainty. Precipitation trends investigated reveal no evidence of climate change effect, due to limited records. It is suggested that confidence limits are used instead. Urban networks designed for low return periods is difficult to be upgraded. Main watercourses' flood protection design has to account for the anticipated worsening of runoff to achieve the required level of flood protection and resilience. Case studies for two major streams in Greece are presented.